1. Field of the Invention
The invention relates generally to membranes, and more specifically to membranes having beneficial combinations of permeation flux and selectivity.
2. Description of the Related Art
A paradox for prior art membranes is the lack of mechanisms that could enable both high molecular separation selectivity and high permeation flux across the membrane. The state-of-the-art zeolite-based or polymer-zeolite hybrid membranes both require a pore size of less than 0.5 nm to enable high selectivity, but suffer from a loss of permeation flux. There is a need for an alternative membrane design and fabrication methodology that does not rely solely on the pore size.
One class of mesoporous (pore size of about 4 nm) glass membrane or support material is VYCOR®, which is an open-cell, porous glass with an internal surface area of approximately 250 square meters per gram. The glass is typically in the form of tubes, having an internal diameter of about 5 mm and a wall thickness of about 1 mm. Because of the wall thickness, this material can suffer from low permeance that limits the overall membrane performance. Again, the separation mechanism of this glass membrane is based on pore size. Membranes having considerably higher permeance are needed for industrial large-throughput processing applications.
For the sake of clarity, it is noted that, generally, the membrane “permeation flux” is defined as the volume flowing through the membrane per unit area per unit time. The SI unit used is m3/m2·s although other units are often used as well. The detailed description of this disclosure provides additional information. The “permeability coefficient”, P (or simply the “permeability”) is defined as the transport flux of material through the membrane per unit driving force per unit membrane thickness. Its value must be experimentally determined. The “permeance” is defined as the ratio of the permeability coefficient (P) to the membrane thickness (L). The permeance for a given component diffusing through a membrane of a given thickness is analogous to a mass transfer coefficient.
No current method uses sputtering to create a supported phase separated glass material, which upon further processing (i.e., acid leaching or etching) produces a superhydrophobic, nanoporous glass membrane layer supported on a porous solid substrate. The prior art is limited to a pore size based separation mechanism and does not provide a superhydrophobic membrane surface to enable a new and improved molecular separation mechanism. Additionally, past developments have been mainly for water-permeating membranes. There is a need for preferential ethanol permeation.